Semiconductor package having an interfacial adhesive layer

ABSTRACT

A semiconductor package has a substrate ( 8 ) and a semiconductor die ( 2 ). The substrate ( 8 ) includes a plurality of contact pads ( 9 ) on its upper surface and a second plurality of external contact areas ( 10 ) on its bottom surface. The semiconductor die ( 2 ) includes an active surface with a plurality of die contact pads ( 3 ) electrically connected by conducting means ( 4 ) to contact pads ( 9 ) on the substrate ( 8 ) and a layer of first adhesive means ( 5 ) on the upper surface ( 18 ) of the die ( 2 ). Mold material ( 15 ) covers the first adhesive means ( 5 ), the die ( 2 ) and the upper surface of the substrate ( 8 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending InternationalApplication No. PCT/IB2004/000990 filed Mar. 16, 2004 which designatesthe United States.

TECHNICAL FIELD

The invention relates to a semiconductor package and a method ofassembling a semiconductor package.

BACKGROUND

DE 102 13 296 A1 discloses a semiconductor package including a chipmounted using the flip-chip technique to a substrate. The chip isembedded in a plastic molding compound. The reliability andmanufacturing yield rate of these packages may be improved.

SUMMARY

A more reliable semiconductor package and a simple cost-effective methodfor producing the package can be provided by providing a semiconductorwafer which includes a plurality of semiconductor dies and a pluralityof sawing streets in its upper surface. Each die may include an activeupper surface with a plurality of die contact pads and conducting meanssuch as solder balls or bumps connected to each die contact pad.

A layer of first adhesive means can be attached to the back side of thewafer, a release film to tape or foil can be attached to the firstadhesive means and a wafer sawing base tape can be attached to therelease film. The dies can then be separated from the wafer by cuttingthrough the wafer from the upper surface using the sawing streetsincluded in the upper surface of the wafer to guide the saw. The layerof first adhesive means and the release film can be cut during thisprocess so that each separated die includes an individual layer of firstadhesive means and a release film. All of the dies are still attached tothe wafer sawing base tape.

A substrate, such as a redistribution board, can be provided whichincludes a plurality of contact pads on its upper surface and a secondplurality of external contact areas on its bottom surface which areelectrically connected by conducting traces on the upper and lowersurface and conducting vias.

The die can be removed from the wafer sawing base tape and mounted ontothe substrate with its active surface facing the substrate so that thesolder bumps are attached to the upper contact areas. The die can thenbe underfilled by underfill material. The release film is then removedfrom the adhesive layer on top of the upper side of the die. Theadhesive layer, die and the upper surface of the substrate by moldmaterial which comprises materials known in the art, such as plastic.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the drawings.

FIG. 1 shows a semiconductor wafer including a plurality of dies andtapes on the back side of the wafer,

FIG. 2 shows the separating of the dies from the wafer of FIG. 1,

FIG. 3 shows the mounting and underfilling of a die of FIG. 2 on asubstrate,

FIG. 4 shows the removal of the release film from the die of FIG. 3,

FIG. 5 shows the encapsulation of the die of FIG. 4 and attachment ofexternal connections to form a semiconductor package.

DETAILED DESCRIPTION

Preferably, the die may be removed from the wafer sawing tape leavingthe first adhesive means attached to the upper side of the die and therelease film attached to the first adhesive means. Advantageously, therelease tape can then act as a protective layer during the underfillprocess step. Excess underfill material may spilt or overflow onto therelease film which forms the outer surface of the upper surface of thedie during this stage of the method. The release film therefore protectsthe upper surface of the die. This may be advantageous as the excessunderfill material is more easily removed from the release film thanfrom the upper surface of the die.

Preferably, the release film can be removed leaving the first adhesivemeans attached to the upper side of the die. The removal of the releasefilm advantageously leads to the removal of the excess underfillmaterial. More preferably, the release film may be removed by anadhesive-coated de-taping film. This is a simple method and avoids theuse of solvents or water to dissolve or loosen the release film. This isadvantageous in that the die, layer of first adhesive means andsubstrate are not damaged by chemical processes.

Alternatively, excess underfill material may be removed from thebackside or upper side of the die by plasma etching using a protectivetemplate, sandblasting using a protective template, grinding, a dry andwet chemical etch of the backside or upper surface of the die using aprotective template or a 2 layer coating, which may be dry or wet, onthe upper surface or back side of the die.

The back side of the wafer can preferably be thinned by known methodssuch as plasma etching or grinding or wet and dry chemical etching. Eachprocess results in a different surface finish on the back side of thewafer, for example, a different surface roughness. In known processes,the mold material and processing conditions are adjusted and optimisedfor each type of surface finish. Wafers having a different surfacefinish or surface roughness may be used in the same manufacturing line.The mold process step is re-optimised for each surface finish which istime-consuming and expensive. A non-optimised process leads todelamination of the mold material from the die surface and to failure ofthe package.

The method according to an embodiment may advantageously leave a layerof first adhesive means attached to the upper surface of the die orinterfacial adhesive layer. This may provide a more uniform andhomogenous outer surface and provides an outer surface to the die whichhas an improved interfacial adhesion or bonding to the mold compound.The reliability and performance of the packages made using the methodaccording to an embodiment are therefore improved. The yield rate of themanufacturing process is also improved. The manufacturing of packages issimplified in that the mold process can be used for wafers thinned usingdifferent methods. Optimisation of the properties of the mold compoundto different surface finish on different wafers is avoided.

An intermediate assembly according to the method according to anembodiment comprises a substrate and a semiconductor die. The substrate,such as a redistribution board, comprises a plurality of contact pads onits upper surface and a second plurality of external contact areas onits bottom surface. The semiconductor die includes an active surfacewith a plurality of die contact pads electrically connected byconducting means to contact pads on the substrate.

The intermediate assembly also includes a layer of first adhesive meansattached to the upper side of the die and a release film attached to thefirst adhesive means.

A semiconductor package may comprise a substrate and a semiconductordie. The substrate, such as a redistribution board, comprises aplurality of contact pads on its upper surface and a second plurality ofexternal contact areas on its bottom surface. The semiconductor dieincludes an active surface with a plurality of die contact padselectrically connected by conducting means to contact pads on thesubstrate. A layer of first adhesive means covers the upper surface ofthe die. Mold material covering the double-sided adhesive, die and uppersurface of the substrate.

The layer of first adhesive attached to the upper surface of the die inthe semiconductor package according to an embodiment may beadvantageous. It provides an interfacial adhesive layer and improvedinterfacial adhesion or bonding between the die and the mold materialand reduces the difference in thermal expansion coefficient between thematerial of the semiconductor die and the mold material.

Preferably, the first adhesive can be a double-sided adhesive and therelease film is non-adhesive. The first adhesive preferably may comprisea double-sided adhesive foil or tape or film. Alternatively, the firstadhesive comprises a flexible adhesive means or semi-solid paste or afluid form. The first adhesive therefore has good adhesion to the uppersurface of the die and also provides an adhesive surface so that therelease film adheres to the first layer. More preferably, the firstadhesive may comprise silica filled rubber, acrylic, polyurethane orepoxy resin and the release film comprises polyester, polyolefin or apolymer.

The die preferably may comprise a thickness of approximately 25 μm toapproximately 800 μm or preferably approximately 50 μm to approximately400 μm or even more preferably approximately 50μm to approximately200μm. A thin die can be advantageous in that the size of thesemiconductor package is reduced leading to a desired miniaturization.

The layer of first adhesive means preferably may comprise a thickness ofapproximately 1 μm to approximately 200 μm or more preferablyapproximately 2 μm to approximately 100 μm or even more preferablyapproximately 5 μm to approximately 50 μm. The thickness and propertiesof the layer of the first adhesive means is adjusted to provide auniform and homogeneous outer surface and improved matching of thethermal expansion coefficient of the semiconductor and mold material.

The use of the release tape in the method according to an embodiment maybe very advantageous. It provides a protective layer so that excessunderfill material does not come into contact with the upper surface ofthe adhesive layer which form the outer surface of the die. The releasetape is easily removed using an adhesive-coated de-taping film so thatthe underfill material which is spilt or overflows onto the release filmis removed but the layer of first adhesive means remains attached to thedie.

The protective layer on the upper surface of the die in thesemiconductor package according to an embodiment can be veryadvantageous. It provides a consistent surface and provides goodinterfacial adhesion to the mold compound. This reduces delaminationbetween the die and the mold material and improves the adhesion. Thisenables a simpler manufacturing process in which the processingparameters are more flexible, the yield loss of the manufacturingprocess is decreased and the reliability of the package improved. Theyield loss is in particular improved for thinner die, which have athickness of less than approximately 200 μm, where the overflow ofunderfill material onto the upper surface of the die is more likely.

FIG. 1 shows a semiconductor wafer 1 which includes a plurality ofsemiconductor dies 2 and tapes or films or foils attached to the backside 11 of the wafer 1. Each die 2 includes an active surface with aplurality of die contact pads 3 and microscopic solder bumps 4 connectedto the die contact pads 3 and a passive surface. Microscopic is usedhere to describe solder bumps which are seen with the aid of amicroscope. The dies 2 are arranged in a regular array of rows andcolumns. A plurality of sawing streets 19, which are also arranged inrows and columns, mark the position of each die 2. A layer of adhesivemeans 5, such as a double-sided comprising silica filled synthesizedrubber, is deposited on the back side 11 of the wafer 1. A release film6 comprising polyester is attached to the double-sided adhesive layer 5.A wafer sawing base tape 7 then is attached to the release film 6.

FIG. 2 shows the next step of the method according to an embodiment. Thedies 2 are separated from the wafer 1 using the sawing streets 19 as aguide for the saw. The dies 2 are separated from the wafer 1 by cuttingfrom the sawing streets 19 in the upper surface of the wafer 1 downwardsinto the wafer 1 and through the double-sided adhesive layer 5 andrelease film 6 and partly into the wafer sawing base tape 7. The wafersawing base tape 7 provides a continuous tape onto which all of theseparated dies 2 are attached. Each separated or individual die 2includes an adhesive layer 5 on its upper passive surface and a releasefilm 6 attached to the adhesive layer 5.

FIG. 3 shows the next step of the process in which the separated dies 2are mounted to a substrate 8 using the flip-chip technique.

The substrate 8, such as a redistribution board, comprises a pluralityof upper contact pads 9 on its upper surface and a second plurality ofexternal contact areas 10 on its bottom surface. The substrate 8 alsoincludes conductive traces on its upper and lower surfaces electricallyconnected by conducting vias (not shown in the figure for clarity) whichelectrically connect the upper contact pads 9 with the external contactpads 10. The die 2 is removed from the wafer sawing tape 7 and ismounted with its active surface facing the substrate 8 so that themicroscopic solder bumps 4 are attached to the upper contact areas 9 onthe substrate. The microscopic solder bumps 4 form an electrical contactbetween the die 2 and the substrate 8. The passive surface of the diefaces upwards away from the substrate 8.

After the die 2 has been removed from the wafer sawing tape 7 andmounted onto the substrate 8, the double-sided adhesive 5 remainsattached to the upper side 18 of the die 2 and the release film 6remains attached to the double-sided adhesive 5.

The area between the active surface of the die 2 and the substrate 8 isunderfilled with underfill material 12 so that the microscopic solderbumps 4 and sides of the die 2 are covered with the underfill material12. During this process some excess underfill 13 spills over onto theupper surface of the release film 6 attached to the adhesive layer 5 onthe upper side 18 of the die 2.

FIG. 4 shows the next step of the process during which the excessunderfill 13 is removed from the upper side 18 of the die 2 using ade-taping film 14 comprising adhesive coated polyolefin. The adhesivecoating of the de-taping film 14 is attached to the release film 6 whichis attached to the adhesive layer 5 on the upper surface 18 of the die2. The de-taping film 14 is removed, thereby removing the release film 6from the upper surface of the die 2 and any excess underfill material 13which spilt onto the release film 6. The double-sided adhesive 5 remainsattached to the upper passive surface 18 of the die 2.

FIG. 5 shows the next stage of the method to form a semiconductorpackage 17 according to an embodiment. The layer of double-sidedadhesive 5 on the upper surface 18 of the die 2 and the upper surface ofthe substrate 8 is encapsulated by mold material 15. External conductingmeans, such as solder balls, 16 are attached to the external contactareas 10 on the bottom surface of the substrate 8. The solder balls 16provide the electrical connection between the package 17 and an externalsubstrate such as a printed circuit board (not shown in the Figure forclarity).

The semiconductor package 17 assembled using the method according to anembodiment and shown in FIG. 5 comprises a substrate 8 and asemiconductor die 2. The substrate 8 comprises a redistribution boardand includes a plurality of contact pads 9 on its upper surface and asecond plurality of external contact areas 10 on its bottom surface. Thesemiconductor die 2 includes an active surface with a plurality of diecontact pads 3 electrically connected by conducting means 4 to contactpads 9 on the substrate 8. The upper surface of the die 2 is covered bya layer of double-sided adhesive 5 or interfacial adhesive layer. Theupper side 18 of the die and the upper surface of the substrate 3 arecovered by mold material 15. Solder balls 16 are attached to theexternal contact areas 10 on the bottom surface of the substrate 8.

The semiconductor packages 17 are then tested, packaged and mounted onan external circuit such as a printed circuit board.

REFERENCE NUMBERS

-   1 wafer-   2 die-   3 die contact pad-   4 microscopic solder bump-   5 double-sided adhesive-   6 release film-   7 wafer sawing base tape-   8 substrate-   9 upper contact areas-   10 external contact areas-   11 back side of wafer-   12 epoxy underfill-   13 excess underfill-   14 de-taping film-   15 mold material-   16 solder balls-   17 semiconductor package-   18 upper side of die-   19 sawing street

1. A method to assemble a semiconductor package comprising the followingsteps: providing a wafer including a plurality of semiconductor dies,each including an active surface with a plurality of die contact padsand a plurality of conducting means attached to the die contact pads,attaching a layer of first adhesive means on the back side of the wafer,attaching a release film to the first adhesive means, attaching a wafersawing base tape to the release film, separating the dies from thewafer, removing the dies from the wafer sawing tape, providing asubstrate comprising a plurality of contact pads on its upper surfaceand a second plurality of external contact areas on its bottom surface,mounting the die onto the substrate with its active surface facing thesubstrate so that the conducting means are attached to the upper contactareas, underfilling the die, removing the release film, andencapsulating the upper side of the die and the upper surface of thesubstrate by mold material.
 2. A method to assemble a semiconductorpackage according to claim 1, wherein the wafer sawing tape is removedleaving the first adhesive means (5) attached to the upper side of thedie and the release film attached to the first adhesive means.
 3. Amethod to assemble a semiconductor package according to claim 1, whereinthe release film is removed leaving the first adhesive means attached tothe upper side of the die.
 4. A method to assemble a semiconductorpackage according to claim 1, wherein the release film is removed by ade-taping film.
 5. A method to assemble a semiconductor packageaccording to claim 1, wherein excess underfill material is removed fromthe upper side of the die by removing the release film or plasma etchingwith a protective template or sandblasting with a protective template orgrinding or dry and wet chemical etching with a protective template or 2layer dry or wet coating on the back side of the die.
 6. A method toassemble a semiconductor package according to claim 1, wherein the backside of the wafer is thinned by plasma etching or grinding or wet anddry chemical etching.
 7. An intermediate assembly comprising: asubstrate comprising a plurality of contact pads on its upper surfaceand a second plurality of external contact areas on its bottom surface,a semiconductor die including an active surface with a plurality of diecontact pads electrically connected by conducting means to contact padson the substrate, a layer of first adhesive means attached to the upperside of the die, and a release film attached to the first adhesivemeans.
 8. An intermediate assembly according to claim 7, wherein thefirst adhesive means is a double-sided adhesive and the release film isnon-adhesive.
 9. An intermediate assembly according to claim 7, whereinthe first adhesive means comprises silica filled rubber or acrylic orpolyurethane or epoxy resin and the release film comprises polyester orpolyolefin or polymer.
 10. An intermediate assembly according to claim7, wherein the die comprises a thickness of approximately 25 μm toapproximately 800 μm or approximately 50 μm to approximately 400 μm orapproximately 50 μm to approximately 200 μm.
 11. An intermediateassembly according to claim 7, wherein the layer of first adhesive meanscomprises a thickness of approximately 1 μm to approximately 200 μm orapproximately 2 μm to approximately 100 μm or approximately 5 μm toapproximately 50 μm.
 12. A semiconductor package comprising: a substratecomprising a plurality of contact pads on its upper surface and a secondplurality of external contact areas on its bottom surface, asemiconductor die including an active surface with a plurality of diecontact pads electrically connected by conducting means to contact padson the substrate, a layer of first adhesive means on the upper surfaceof the die, and mold material covering the first adhesive means, the dieand the upper surface of the substrate.
 13. A semiconductor packageaccording to claim 12, wherein the die comprises a thickness ofapproximately 25 μm to approximately 800 μm or approximately 50 μm toapproximately 400 μm or approximately 50 μm to approximately 200 μm. 14.A semiconductor package according to claim 12, wherein the layer offirst adhesive means comprises a thickness of approximately 1 μm toapproximately 200 μm or approximately 2 μm to approximately 100 μm orapproximately 5 μm to approximately 50 μm.
 15. A semiconductor packageaccording to claim 12, wherein the first adhesive means comprises silicafilled synthesized rubber or acrylic or polyurethane or epoxy resin.